One of the most tired cliches is that so-and-so doesn't actually sell such-and-such; they sell peace of mind. Well, in this case, it's true. The question is whether there is a market for that peace of mind among airline customers.

In recent months, two companies — Chicago-based Options Away (www.optionsaway.com) and San Francisco-based Level Skies (www.levelskies.com) — have begun offering the chance to lock in airfares without committing to a ticket.

This sort of service has been bubbling at the industry edges in various incarnations; Kayak (www.kayak.com) and Bing (www.bing.com) pair their flight searches with recommendations on whether to buy or wait. These are statistical projections on whether the cost of a ticket will rise or fall. United, meanwhile, has introduced Fare Lock, which allows consumers to hold a fare for as long as seven days for a fee.

Options Away and Level Skies merge the two strategies by using statistical projections to decide how much to charge to hold a given fare.

Options Away, which serves U.S. and some Canadian cities, is relatively straightforward: Enter a route and dates, and the site brings back a price (identical to what the airlines charge) but with an added fee to hold that price for one, three, seven, 14 or 21 days. The cost to hold round-trip tickets ranges from $4 to about $45. (Not all tickets qualify for all lengths of a hold; some might have an option of just a 24-hour hold, which federal regulations require of airlines anyway.)

I asked Heidi Brown, who co-founded Options Away with her husband, Rob, for examples of who might use the service. She cited a traveler who knows the days he wants to travel but not the destination; that person can reserve tickets to two destinations on the same days, then decide which trip to take. Or, she said, it could benefit someone who knows where he wants to go but not the exact days; he can hold tickets for multiple flights on multiple days.

"This takes away the sense of, 'The price on this is going to go up,'" she said.

Level Skies is more complicated. It does serve some foreign destinations but not all.

A traveler enters travel dates and a destination; Level Skies then returns a "flex fare price" that costs about $20 to $40 more than the cheapest fare. The up-charge depends on how long a customer wants to hold a fare (one to four weeks is possible) and the degree of flexibility sought on departure and return days (three-day windows are available on both ends). A downside: The customer doesn't choose the airline or exact time to fly. Those deciding not to keep the ticket get the cost of the ticket refunded minus a fee kept by Level Skies.

"The idea is to make a quick, simple purchase that minimizes the amount of thinking the consumer needs to do," said Ryan Houck, Level Skies chief executive. "It's about locking in the flight now and working out details later."

Options Away and Level Skies say they operate based on proprietary algorithms that use several factors, such as historical costs and route details, to decide which fares it can guarantee and at what cost.

In that sense, both companies offer the aforementioned peace of mind; if you're not ready to commit to a flight, you can lock in a price without worrying that it will soon spike. If the price decreases, the difference is refunded. If the price does rise, that's only a concern for Options Away or Level Skies. Both companies are confident that their algorithms will make them come out on top more often than not.

But is that peace of mind worth it? To the savviest travelers who are comfortable searching for fares, have a sense of where and when they want to go and know a good deal when they see it, I'm skeptical (though paying a bit to keep multiple options open seems reasonable).

Houck and Brown concede that their industry is new enough to be in swift transition and that both websites and their offerings could change; both also hope to partner with online travel companies such as Kayak or Orbitz.